Abstract: A meteorological balloon having improved wind measurement during an ascent stage, includes an inflatable envelope having, during ascent, an upper hemisphere and a lower hemisphere, and presenting an outer surface, a GPS type sonde secured to the inflatable envelope, and a device for improving wind measurement which is a single spoiler secured to the upper hemisphere portion envelope. The spoiler is constructed and arranged to transmit any aerodynamic force acting thereon to the balloon and to modify air streams following the outside surface of the balloon so as to prevent the air streams from adhering to the outer surface of the bottom hemisphere of the balloon during ascent.